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United States Patent |
6,054,251
|
Imai
,   et al.
|
April 25, 2000
|
Photopolymerizable composition
Abstract
The present invention provides a visible laser-curable resist composition
which contains at least one radical-protecting compound selected from a
phosphorous acid ester compound and an aromatic compound having
N,N-dimethylamino group bonded to the carbon atom forming the aromatic
ring and which is free from the hindrance of curing caused by deactivation
of radical by oxygen and has excellent curability, and a process for
formation of a resist pattern using the above composition.
Inventors:
|
Imai; Genji (Hiratsuka, JP);
Kogure; Hideo (Atsugi, JP)
|
Assignee:
|
Kansai Paint Co., Ltd. (Hyogo-Ken, JP)
|
Appl. No.:
|
936840 |
Filed:
|
September 25, 1997 |
Foreign Application Priority Data
Current U.S. Class: |
430/285.1; 430/195; 430/281.1; 430/286.1; 430/287.1; 430/325; 430/919; 522/10; 522/14; 522/26; 522/28; 522/902 |
Intern'l Class: |
G03F 007/031; G03F 007/038; G03F 007/30 |
Field of Search: |
430/281.1,287.1,286.1,919,195,285.1,947,917,920,922,926,325
522/10,14,28,902,26
|
References Cited
U.S. Patent Documents
3418295 | Dec., 1968 | Schoenthaler | 430/285.
|
4055430 | Oct., 1977 | Hasegawa et al. | 96/90.
|
4071424 | Jan., 1978 | Dart et al. | 204/159.
|
4500629 | Feb., 1985 | Irving et al. | 430/286.
|
4563438 | Jan., 1986 | Berner et al. | 430/281.
|
4782100 | Nov., 1988 | Iwamoto et al. | 522/120.
|
4849321 | Jul., 1989 | Hung et al. | 430/284.
|
4970135 | Nov., 1990 | Kushi et al. | 430/280.
|
5068371 | Nov., 1991 | Steiner et al. | 556/53.
|
5322762 | Jun., 1994 | Kushi et al. | 430/288.
|
5514521 | May., 1996 | Kobayashi et al. | 430/281.
|
5639802 | Jun., 1997 | Neckers et al. | 522/25.
|
5721288 | Feb., 1998 | Aotani et al. | 522/12.
|
5882843 | Mar., 1999 | Kudo et al. | 430/285.
|
Foreign Patent Documents |
WO 97/28194 | Aug., 1997 | WO.
| |
Other References
Registry No. 7478-69-5, Registry File of Americon Chemical Society obtained
from STN Database Service, 1998.
|
Primary Examiner: Hamilton; Cynthia
Attorney, Agent or Firm: Wenderoth, Lind & Ponack, L.L.P.
Claims
We claim:
1. A photopolymerizable composition comprising:
a photocuring acrylic resin having a (meth)acryloyl group as a
photosensitive group, which is obtained by adding a glycidyl
group-containing polymerizable unsaturated compound to an acrylic resin of
high acid value;
a photopolymerization initiator effective to promote curing of the resin
upon exposure to a visible light, which is a combination of a compound
represented by the following formula:
##STR9##
wherein R.sup.4, R.sup.5, R.sup.6 and R.sup.7 are each independently an
alkyl group of 1-3 carbon atoms, with a titanocene compound; and
at least one radical-protecting compound which is an aromatic compound
having N,N-dimethylamino group bonded to the carbon atom forming the
aromatic ring.
2. A photopolymerizable composition according to claim 1, wherein the
aromatic compound having N,N-dimethylamino group bonded to the carbon atom
forming the aromatic ring is an unsubstituted or substituted
N,N-dimethylaniline.
3. A photopolymerizable composition according to claim 2, wherein the
unsubstituted or substituted N,N-dimethylaniline is selected from the
group consisting of N,N-dimethylaniline, 4-bromo-N,N-dimethylaniline,
4-tert-butyl-N,N-dimethylaniline, 2,6-diisopropyl-N,N-dimethylaniline,
4,4'-vinylidenebis(N,N-dimethylaniline),
4,4'-methylenebis(N,N-dimethylaniline),
4,4'-methylenebis(2,6-diisopropyl-N,N-dimethylaniline),
N,N,2,4,6-pentamethylaniline, N,N-dimethyl-m-toluidine,
4-(2-pyridylazo)-N,N-dimethylaniline and N,N-dimethyl-4-nitrosoaniline.
4. A photopolymerizable composition according to claim 1, wherein the
radical-protecting compound is an aromatic compound of 120-400 molecular
weight having N,N-dimethylamino group bonded to the carbon atom forming
the aromatic ring.
5. A photopolymerizable composition according to claim 1, containing the
radical-protecting compound in an amount of 0.1-30 parts by weight per 100
parts by weight (as solid content) of the composition.
6. A photopolymerizable composition according to claim 1, further
comprising an ethylenically unsaturated compound.
7. A photopolymerizable composition according to claim 6, comprising the
photopolymerization initiator in an amount of 0.1-10 parts by weight per
100 parts by weight of the total of the photocuring resin and the
ethylenically unsaturated compound.
8. A process for formation of a resist pattern, which comprises forming, on
a substrate, a resist film made of a photopolymerizable composition of
claim 1, then pattern-wise applying a visible laser to the resist film,
and subjecting the visible laser-exposed resist film to development.
9. A process for formation of a resist pattern, which comprises forming, on
a substrate, a resist film made of a photopolymerizable composition of
claim 1, forming an oxygen-shielding layer on the resist film, then
pattern-wise applying a visible laser to the resist film via the
oxygen-shielding layer, and subjecting the visible laser-exposed resist
film to development.
10. A resist film formed from a photopolymerizable composition of claim 1.
11. A photopolymerizable composition according to claim 1, wherein the
photocuring acrylic resin having a (meth)acryloyl group has a molecular
weight of 1,000-100,000 and the amount of (meth)acryloyl group of 0.2 to 5
moles/kg resin.
12. A photopolymerizable composition according to claim 1, wherein the
acrylic resin of high acid value has an acid value of about 40-760.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a photopolymerizable composition which is
improved in hindrance of curing caused by deactivation of radical by
oxygen and which has excellent curability, and also to a process for
formation of a resist pattern from the composition by exposing the
composition to a visible laser.
2. Description of the Prior Art
To form a conductor circuit of, for example, printed wiring board, it has
been conducted to coat a photosensitive resist on a substrate, subjecting
the resulting resist film to light exposure and development to form a
resist pattern, and subjecting the resist pattern to etching to remove the
unnecessary portion of the substrate.
The above light exposure is conducted by, for example, light exposure via a
photomask or direct drawing using a laser. The light exposure via a
photomask has problems, for example, in that a considerable time is needed
for the positioning of the photomask and that the positioning of the
photomask is difficult when the resist has surface tackiness.
The direct drawing using a laser requires a highly sensitive resist because
the time of laser application is very short. Therefore, so that the active
radical generated in the resist by laser application is not deactivated by
the oxygen in air and the resist can maintain the high sensitivity, it is
generally conducted to cover the surface of the resist with an
oxygen-shielding layer (e.g. a cover coating layer or a cover film layer).
The present inventors made a study with a view to developing a resist
usable in the direct drawing using a visible laser, in which resist the
active radical generated by laser application is hardly deactivated by the
oxygen in air and consequently the sensitivity of the resist can be
maintained. As a result, it was found out that the above object can be
achieved by allowing a resist to contain a particular radical-protecting
compound. The present invention has been completed based on the finding.
SUMMARY OF THE INVENTION
According to the present invention, there is provided a photopolymerizable
composition containing at least one radical-protecting compound selected
from a phosphorous acid ester compound and an aromatic compound having
N,N-dimethylamino group bonded to the carbon atom forming the aromatic
ring.
According to the present invention, there is also provided a process for
formation of a resist pattern, which comprises forming, on a substrate, a
resist film made of the above photopolymerizable composition, then
pattern-wise applying a visible laser to the resist film, and subjecting
the visible laser-exposed resist film to development.
According to the present invention, there is also provided a process for
formation of a resist pattern, which comprises forming, on a substrate, a
resist film made of the above photopolymerizable composition, forming an
oxygen-shielding layer on the resist film, then pattern-wise applying a
visible laser to the resist film via the oxygen-shielding layer, and
subjecting the visible laser-exposed resist film to development.
DETAILED DESCRIPTION OF THE INVENTION
The photopolymerizable composition of the present invention (hereinafter
referred to as "resist composition" in some cases) can be any resist
composition of negative type which is cured upon exposure to light (e.g. a
visible laser), if the radical-protecting compound contained in the
present photopolymerizable composition is excluded. The present
composition may be a liquid resist or a dry film resist.
Representative examples of the present resist composition are those
obtained by adding a particular radical-protecting compound to a system
comprising a photocuring resin having photosensitive group crosslinkable
or polymerizable upon light exposure, a polymerization initiator effective
to a visible light and, as necessary, an ethylenically unsaturated
compound.
The photosensitive group of the photocuring resin includes, for example,
acryloyl group, methacryloyl group, cinnamoyl group, allyl group, azido
group and cinnamylidene group. A preferable molecular weight of the
photocuring resin is generally 1,000-100,000, preferably 3,000-50,000. A
preferable amount of the photosensitive group of the photocuring resin is
0.2-5 moles/kg resin, particularly 3-5 moles/kg resin.
The photosensitive group of the photocuring resin is preferably acryloyl
group or methacryloyl group. The photocuring resin having such
photosensitive group can be obtained, for example, by adding a glycidyl
group-containing polymerizable unsaturated compound (e.g. glycidyl
methacrylate or glycidyl acrylate) to a carboxyl group-containing resin
having a high acid value of preferably about 40-760, more preferably about
100-700, to introduce acryloyl group or methacryloyl group into the resin.
The resin of high acid value includes, for example, an acrylic resin of
high acid value and a polyester resin of high acid value. An acrylic resin
of high acid value is particularly preferred.
The photopolymerization initiator effective to a visible light includes,
for example, a combination of a hexaarylbisimidazole with a
p-dialkylaminobenzylidene ketone or a dialkylaminochalcone [Japanese
Patent Application Laid-Open No. 155292/1979 (corresponding to U.S. Pat.
No. 4,162,162)], a combination of camphor quinone with a dye [Japanese
Patent Application Laid-Open No. 84183/1973 (corresponding to U.S. Pat.
No. 3,756,827)], a combination of a diphenyliodonium salt with a Michler's
ketone (GB-A-2020297), a combination of a S-triazine type compound with a
merocyanine dye (Japanese Patent Application Laid-Open No. 151024/1979), a
combination of a S-triazine type compound with a thiapyrylium salt
(Japanese Patent Application Laid-Open No. 40302/1983), a combination of
3-ketocoumarin with a titanocene compound [Japanese Patent Application
Laid-Open No. 10602/1988 (corresponding to EP-A-242330)], a combination of
a compound represented by the following general formula:
##STR1##
(wherein R is a lower dialkylamino group such as diethylamino group or the
like, a lower dialkenylamino group or an alicyclic amino group) with a
titanocene compound (Japanese Patent Application Laid-Open No.
239703/1991), a combination of a dialkylaminocoumarin type sensitizer
represented by the following general formula:
##STR2##
(wherein R.sup.1 and R.sup.2, which may be the same or different, are each
a lower alkyl group; and R.sup.3 is a hydrogen atom, a lower alkyl group,
an alkoxyalkyl group, a hydroxy-alkoxyalkyl group or an
alkoxycarbonylalkyl group) with an iron-allene complex or a titanocene
compound [Japanese Patent Application Laid-Open No. 223759/1991
(corresponding to U.S. Pat. No. 5,045,434)], a combination of a compound
represented by the following general formula:
##STR3##
(wherein R.sup.4, R.sup.5, R.sup.6 and R.sup.7 are each independently an
alkyl group of 1-3 carbon atoms such as methyl group or the like) or a
compound represented by the following general formula:
##STR4##
(wherein R.sup.8, R.sup.9 and R.sup.10 are each independently an alkyl
group of 1-3 carbon atoms such as methyl group or the like) with a
titanocene compound, and a combination of one of the above combinations,
with a nitrogen-containing compound such as benzotriazole or the like.
A suitable amount of the polymerization initiator used is generally 0.1-10
parts by weight, particularly 0.5-5 parts by weight per 100 parts by
weight of the total of the photocuring resin and the ethylenically
unsaturated compound described below.
The ethylenically unsaturated compound optionally used in the present
resist composition is a compound having at least one, preferably 1-4
ethylenically unsaturated double bonds, and includes a monomer, a dimer, a
trimer or other oligomer all capable of insolubilizing the exposed portion
of resist by causing addition polymerization when exposed to a light.
Specific examples of such a compound are acrylic acid, methacrylic acid,
ethylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate,
triethylene glycol di(meth)acrylate, tetra- to hexadecaethylene glycol
di(meth)acrylate, propylene glycol di(meth)acrylate, trimethylolpropane
tri(meth)acrylate, pentaerythrithol tetra(meth)acrylate, ethylene glycol
diitaconate, ethylene glycol dimaleate, hydroquinone di(meth)acrylate,
resorcinol di(meth)acrylate, pyrogallol (meth)acrylate, oligourethane
acrylate, oligoepoxy acrylate and divinylbenzene. In the present
specification, "(meth)acrylate" refers to acrylate or methacrylate.
The amount of the ethylenically unsaturated compound used can be generally
200 parts by weight or less, preferably 1-100 parts by weight, more
preferably 3-50 parts by weight per 100 parts by weight of the photocuring
resin. The ethylenically unsaturated compound can be used singly or in
combination of two or more compounds.
The radical-protecting compound used in the present resist composition
hinders the deactivation by oxygen, of the radical generated in the resist
film (formed from the composition) when the film is exposed to a visible
laser for curing, and thereby can allow the resist film to have good
photosensitivity even in the presence of oxygen. In the present invention,
there is used, as the radical-protecting compound, at least one compound
selected from a phosphorous acid ester compound and an aromatic compound
having N,N-dimethylamino group bonded to the carbon atom forming the
aromatic ring.
A photopolymerizable composition generates a radical when exposed to a
light; however, in the presence of oxygen, the radical reacts with oxygen
to form a peroxyradical and these peroxyradical molecules ordinarily react
with each other, resulting in the deactivation of the radical. Meanwhile,
when the photopolymerizable composition contains a radical-protecting
compound according to the present invention, it is presumed that most of
the above-mentioned peroxyradical molecules react with the
radical-protecting compound to form a different radical and this different
radical contributes to the curing reaction of resist film; as a result,
the photopolymerizable composition of the present invention can maintain
high sensitivity even in the presence of oxygen.
Representative examples of the phosphorous acid ester compound can be
dialkyl (C.sub.1-20), diaryl or diaralkyl phosphites such as dimethyl
phosphite, diethyl phosphite, dipropyl phosphite, dibutyl phosphite,
bis(2-ethylhexyl) phosphite, diphenyl phosphite, dibenzyl phosphite and
the like; trialkyl (C.sub.1-20) or triaryl phosphites such as trimethyl
phosphite, triethyl phosphite, triisopropyl phosphite, tributyl phosphite,
trilauryl phosphite, triphenyl phosphite, triisodecyl phosphite,
tris(tridecyl) phosphite and the like; aralkyl dialkyl (C.sub.1-10)
phosphites such as benzyl diethyl phosphite and the like; and
tri(haloalkyl) phosphites such as tris(2,2,2-trifluoroethyl) phosphite,
tris(2-chloroethyl) phosphite and the like.
Representative examples of the aromatic compound having N,N-dimethylamino
group bonded to the carbon atom forming the aromatic ring can be
N,N-dimethylaniline derivatives such as N,N-dimethylaniline,
4-bromo-N,N-dimethylaniline, 4-tert-butyl-N,N-dimethylaniline,
2,6-diisopropyl-N,N-dimethylaniline,
4,4'-vinylidenebis(N,N-dimethylaniline),
4,4'-methylenebis(N,N-dimethylaniline),
4,4'-methylenebis(2,6-diisopropyl-N,N-dimethylaniline),
N,N,2,4,6-pentamethylaniline, N,N-dimethyl-m-toluidine,
4-(2-pyridylazo)-N,N-dimethylaniline, N,N-dimethyl-4-nitrosoaniline and
the like.
Of the above aromatic compounds, those having a molecular weight of 120-400
are particularly preferred in view of their compatibility with the resist
resin and the sensitivity of the resulting resist film to visible light.
The amount of the radical-protecting compound used is not particularly
restricted and can be varied depending upon, for example, the kind and
amount of the photopolymerization initiator used; however, an appropriate
amount, when viewed from the photosensitivity of the resist film, the
strength of the cured film, etc., is generally 0.1-30 parts by weight,
preferably 0.5-20 parts by weight, more preferably 1-10 parts by weight
per 100 parts by weight of the solid content of the resist composition.
The resist composition of the present invention can further comprise, as
necessary, an adhesion promoter; a photopolymerization initiator and a
sensitizer both effective to ultraviolet light; a polymerization inhibitor
such as hydroquinone, 2,6-di-tert-butyl-p-cresol (BHT),
N,N-diphenyl-p-phenylenediamine or the like; organic resin fine particles;
a pigment such as coloring pigment, extender pigment or the like; a metal
oxide such as cobalt oxide or the like; a plasticizer such as dibutyl
phthalate, dioctyl phthalate, tricresyl phosphate, polyethylene glycol,
polypropylene glycol or the like; an organic solvent; and so forth.
The adhesion promoter is used in order to increase the adhesivity of resist
film to substrate. As the adhesion promoter, there can be mentioned, for
example, tetrazoles such as tetrazole, 1-phenyltetrazole,
5-aminotetrazole, 5-amino-1-methyltetrazole, 5-amino-2-phenyltetrazole,
5-mercapto-1-phenyltetrazole, 5-mercapto-1-methyltetrazole,
5-methylthiotetrazole, 5-chloro-1-phenyl-1H-tetrazole and the like.
As the photopolymerization initiator effective to ultraviolet light, there
can be mentioned, for example, acetophenones such as diethoxyacetophenone,
2-hydroxy-2-methyl-1-phenylpropane-1-one, benzyl dimethyl ketal,
1-(4-isopropylphenyl)-2-hydroxy-2-methylpropane-1-one,
4-(2-hydroxyethoxy)phenyl (2-hydroxy-2-propyl) ketone, 1-hydroxycyclohexyl
phenyl ketone, 1-phenyl-1,2-propanedione-2-(o-ethoxycarbonyl)oxime,
2-methyl-2-morpholino-(4-thiomethylphenyl)propane-1-one,
2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)butanone and the like;
benzoin ethers such as benzoin, benzoin methyl ether, benzoin ethyl ether,
benzoin isopropyl ether, benzoin isobutyl ether and the like;
benzophenones such as benzophenone, methyl o-benzoylbenzoate,
4-phenylbenzophenone, 4,4'-dichlorobenzophenone, hydroxybenzophenone,
4-benzoyl-4'-methyldiphenyl sulfide, alkylbenzophenone,
3,3',4,4'-tetra(tert-butylperoxycarbonyl)-benzophenone,
4-benzoyl-N,N-dimethyl-N-[2-(1-oxo-2-propenyloxy)ethyl)benzenemethanaminiu
m bromide, (4-benzoylbenzyl)trimethylammonium chloride,
2-hydroxy-3-(4-benzoylphenoxy)-N,N,N-trimethyl-1-propanaminium chloride
monohydrate and the like; thioxanthones such as 2-isopropylthioxanthone,
2,4-dimethylthioxanthone, 2,4-diethylthioxanthone,
2,4-dichlorothioxanthone,
2-hydroxy-3-(3,4-dimethyl-9-oxo-9H-thioxanthene-2-yloxy)-N,N,N-trimethyl-1
-propanaminium chloride and the like;
2,4,6-trimethylbenzoyldiphenylphosphine oxide;
2,2'-bis((o-chlorophenyl)-4,5,4',5'-tetraphenyl-1,2-biimidazole;
10-butyl-2-chloroacridone; 2-ethylanthraquinone; 1,2-diphenylethane;
9,10-phenanthrenequinone; camphorquinone; and methylphenylglyoxy ester.
These compounds can be used singly or as a mixture of two or more
compounds.
In some cases, the above photopolymerization initiator can be used in
combination with a sensitizer, whereby higher sensitivity to ultraviolet
light can be obtained. As such a sensitizer, there can be used known
sensitizers such as triethanolamine, methyidiethanolamine,
triisopropanolamine, methyl 4-dimethylaminobenzoate, ethyl
4-dimethylaminobenzoate, isoamyl 4-dimethylaminobenzoate,
(2-dimethylamino)ethyl benzoate, (n-butoxy)ethyl 4-dimethylaminobenzoate,
2-ethylhexyl 4-dimethylaminobenzoate, Michler's ketone,
4,4'-diethylaminobenzophenone and the like.
The resist composition of the present invention can be produced, for
example, by uniformly mixing the above-mentioned individual components in
an appropriate solvent.
Next, description is made on the process for formation of a resist pattern
from the present resist composition by forming, on a substrate, a visible
laser-curable resist film from the composition and curing the resist film
pattern-wise.
The substrate on or to which the present resist composition is coated or
adhered, is not particularly restricted as long as the resist composition
can be coated thereon or adhered thereto. Representative examples of the
substrate are a glass plate; a substrate obtained by forming, on a glass
plate, a thin film of a metal or metal oxide such as indium-tin oxide
(ITO), chromium, copper or the like; a metal plate such as aluminum plate,
copper plate or the like; a plastic plate such as polycarbonate plate,
acrylic resin plate, glass-epoxy plate or the like; a laminate plate
having a metal layer as the surface layer, such as copper-plated or
copper-clad glass-epoxy plate or the like; and a laminate plate obtained
by making throughholes in the above laminate plate.
Formation of a visible laser-curable resist film on the substrate using the
present resist composition is conducted, for example, as follows. When the
present resist composition is a liquid resist composition, the composition
is coated on a substrate by spray coating, electrostatic coating, roll
coating, curtain flow coating, spin coating, silk screen printing,
dipping, electrodeposition or the like, and the resulting resist film is
dried. When the resist composition is a dry film resist, the protective
film is peeled and the resulting dry film resist is heat-bonded to a
substrate to form a resist film. The dry film resist need not have a cover
film layer but may have it as necessary. The thickness of the resist film
is not particularly restricted and can be determined appropriately
depending upon the application of the resist pattern obtained. A
preferable thickness is 0.5-50 .mu.m, particularly 1-40 .mu.m, more
particularly 3-30 .mu.m in terms of dry film thickness.
Formation of a dry film resist from the present resist composition can be
conducted, for example, by coating the present resist composition on a
transparent film (e.g. a polyester film) (this film later becomes a cover
film layer) by the use of a roll coater, a blade coater, a curtain coater
or the like, drying the resulting resist film, and sticking a protective
film onto the resist layer of the dried resist film.
In the present process for formation of a resist pattern, a visible
laser-curable resist film is formed on a substrate in the above-mentioned
manner; as necessary, an oxygen-shielding layer is formed on the resist
film; then, the resist film is exposed to a visible laser pattern-wise;
thereafter, development is conducted to form a resist pattern.
The oxygen-shielding layer is formed so that the radical generated in the
resist film by light exposure is shielded from the oxygen in air and
prevented from being deactivated by oxygen and thereby the curing of the
resist by light exposure can proceed smoothly. The oxygen-shielding layer
may be a cover coating layer formed on the resist film by coating, or a
cover film layer formed by sticking a film on the resist film. When a dry
film resist is used, only by adhering a dry film resist having a cover
film layer, to a substrate, a cover film layer can be formed simply.
The oxygen-shielding layer is made of a material which is
non-photosensitive, has substantially no tackiness at room temperature,
has oxygen shieldability, and is transparent to a light applied.
Therefore, the material preferably has a glass transition temperature (Tg)
of 20.degree. C. or above, preferably 30-80.degree. C., more preferably
40-70.degree. C.
The oxygen shieldability of the oxygen-shielding layer preferably is
5.times.10.sup.-12 cc. cm/cm.sup.2. sec. cmHg or less, particularly
1.times.10.sup.-12 cc. cm/cm.sup.2. sec. cmHg or less in terms of oxygen
permeability of film. The oxygen permeability is a value measured
according to the method described in ASTM D 1434-82 (1986).
The oxygen-shielding layer is peeled from the resist film after light
exposure and then development is conducted. However, when the peeling is
difficult (when the oxygen-shielding layer is a cover coating layer, the
peeling is generally difficult), the peeling is not conducted and
therefore the oxygen-shielding layer must be dissolved and removed during
development.
As the film-formable resin capable of forming an oxygen-shielding layer
which is soluble and removable during development and which satisfies the
above-mentioned requirements for oxygen-shielding layer, there can be
mentioned, for example, a polyvinyl alcohol, a partially saponified
polyvinyl acetate, a mixture thereof, and a mixture of a polyvinyl alcohol
and a polyvinyl acetate. These resins are preferred because they have
excellent film formability and well soluble in an aqueous developer (e.g.
water, dilute aqueous alkali solution or dilute aqueous acid solution). A
solution (e.g. an aqueous solution) of the above film-formable resin is
coated on a resist film and dried, whereby a cover coating layer can be
formed. A preferable thickness of the cover coating layer is generally
0.5-5 .mu.m, particularly 1-3 .mu.m.
A cover film layer can be formed by attaching a free film of the
above-mentioned film-formable resin to the surface of a resist film. When
the cover film layer is peeled from the surface of the resist film after
light exposure but before development, the cover film layer need not be
soluble in the developer used and may be made of not only the
above-mentioned film-formable resin but also of a polyester (e.g. a
polyethylene terephthalate), an acrylic resin, a polyethylene, a polyvinyl
chloride or the like. A preferable thickness of the cover film layer is
generally 1-70 .mu.m, particularly 2-40 .mu.m.
The resist film formed from the present resist composition, which contains
a radical-protecting compound, can considerably alleviate the inhibition
of curing caused by oxygen even with no oxygen-shielding layer formed
thereon and can maintain good photosensitivity. Formation of an
oxygen-shielding layer, however, can further increase the sensitivity to
visible laser.
Pattern-wise application of a visible laser to the resist film can be
conducted, for example, by direct drawing using a visible laser, such as
scanning of a visible laser based on the CAD data prepared beforehand. The
source of the visible laser includes an Ar ion laser, an excimer laser, a
carbon dioxide laser, etc. An appropriate exposure of the visible laser is
generally 0.1-50 mJ/cm.sup.2, preferably 0.3-30 mJ/cm.sup.2, more
preferably 0.5-10 mJ/cm.sup.2.
The laser application cures the exposed portion of the resist film
(negative type), and the unexposed portion is removed by development.
After the laser application but before development, the resist film may be
heated as necessary for stress relaxation of the resist film or for
promotion of the post-reaction of the generated radical. This heating can
be conducted in a short time by using a hot plate.
Development after the laser application can be conducted by washing the
exposed resist film, for example, by immersing the resist film in a
developer suitable for the kind of the resist film, such as acid
developer, alkali developer, water, organic solvent or the like, or by
spraying the above developer on the resist film. The conditions of
development are not particularly restricted but are generally
15-40.degree. C. for about 15 seconds to 5 minutes. After the development,
water washing is conducted as necessary. The development step removes the
unexposed portion of the resist film, whereby a resist pattern is formed.
After the development step, the resist pattern may be as necessary heated
or exposed to ultraviolet light for further curing. When exposure to
ultraviolet light is employed for further curing, it is preferred to allow
the resist composition to beforehand contain a photopolymerization
initiator and a sensitizer both effective to ultraviolet light.
The resist pattern formed as above according to the present process can be
used per se for decoration or other purposes, but may be used as an
etching resist or as a solder resist.
The resist pattern can be used, for example, in formation of an
electroconductive circuit pattern of printed circuit board. In this case,
a resist pattern is formed according to the present process, on the
electroconductive layer of a laminate plate comprising a substrate and, as
the surface layer, an electroconductive layer made of copper or the like;
using this resist pattern as an etching resist, the exposed portion of the
electroconductive layer (the portion having no resist pattern thereon) is
etched; thereby, a circuit pattern can be formed.
This etching can be conducted using an etchant selected so as to match, for
example, the kind of the electroconductive layer. For example, when the
electroconductive layer is copper, there can be used, as the etchant, an
acidic etchant (e.g. cupric chloride), an ammonia type etchant or the
like.
After the etching step, the remaining resist film is removed to obtain a
printed circuit board. Removal of the remaining resist film is conducted
by dissolving or peeling the resist film, and there can be used a solvent
which is substantially inert to the substrate and the circuit pattern
formed thereon (i.e. the remaining electroconductive layer). The solvent
can be, for example, an aqueous alkali (e.g. sodium hydroxide) solution,
an aqueous acid solution, or one of various organic solvents.
The present invention is hereinafter described specifically by the
following Examples. In the followings, parts and % are by parts by weight
and % by weight, respectively.
PRODUCTION EXAMPLE 1 (production of photocuring resin)
A mixture consisting of 40 parts of methyl methacrylate, 40 parts of butyl
acrylate, 20 parts of acrylic acid and 2 parts of azobisisobutyronitrile
was dropwise added, in 3 hours, to 90 parts of propylene glycol monomethyl
ether kept at 110.degree. C. in a nitrogen gas atmosphere. The resulting
mixture was subjected to aging for 1 hour. Thereto was dropwise added, in
1 hour, a mixture consisting of 1 part of azobisdimethylvaleronitrile and
10 parts of propylene glycol monomethyl ether. The resulting mixture was
subjected to aging for 5 hours to obtain a solution of a high-acid-value
acrylic resin (resin acid value=155 mg KOH/g). To the solution were added
24 parts of glycidyl methacrylate, 0.12 part of hydroquinone and 0.6 part
of tetraethylammonium bromide. The resulting mixture was subjected to a
reaction at 110.degree. C. for 5 hours while blowing air thereinto, to
obtain a photocuring resin solution having a solid content of about 55.4%.
The photocuring resin had a resin acid value of about 50 mg KOH/g, a
polymerizable unsaturated group content of 1.35 moles/kg, a Tg of
20.degree. C. and a number-average molecular weight of about 20,000.
PRODUCTION EXAMPLE 2 (production of photocuring resin)
A mixture consisting of 60 parts of styrene, 10 parts of methyl acrylate,
30 parts of acrylic acid and 3 parts of azobisisobutyronitrile was
dropwise added, in 3 hours, to 90 parts of ethylene glycol monomethyl
ether kept at 120.degree. C. in a nitrogen gas atmosphere. The resulting
mixture was subjected to aging for 1 hour. Thereto was dropwise added, in
1 hour, a mixture consisting of 1 part of azobisdimethylvaleronitrile and
10 parts of ethylene glycol monomethyl ether. The resulting mixture was
subjected to aging for 5 hours to obtain a solution of a high-acid-value
acrylic resin (resin acid value=233 mg KOH/g). To the solution were added
35 parts of glycidyl methacrylate, 0.13 part of hydroquinone and 0.6 part
of tetraethylammonium bromide. The resulting mixture was subjected to a
reaction at 110.degree. C. for 5 hours while blowing air thereinto, to
obtain a photocuring resin solution having a solid content of about 57.4%.
The photocuring resin had a resin acid value of about 70 mg KOH/g, a
polymerizable unsaturated group content of 1.83 moles/kg, a Tg of
45.degree. C. and a number-average molecular weight of about 15,000.
PRODUCTION EXAMPLE 3 (production of photocuring resin)
A mixture consisting of 25 parts of methyl methacrylate, 15 parts of butyl
acrylate, 15 parts of acrylic acid, 45 parts of 2-hydroxyethyl
methacrylate and 2 parts of azobisisobutyronitrile was dropwise added, in
3 hours, to 100 parts of N,N-dimethylformamide kept at 80.degree. C. in a
nitrogen gas atmosphere. The resulting mixture was subjected to aging for
1 hour. Thereto was dropwise added, in 1 hour, a mixture consisting of 1
part of azobisdimethylvaleronitrile and 5 parts of N,N-dimethylformamide.
The resulting mixture was subjected to aging for 5 hours to obtain a
solution of a high-acid-value acrylic resin (resin acid value=115 mg
KOH/g). To 200 parts of the solution was added 120 parts of pyridine.
Then, 207 parts of a solution of 150 parts of N,N-dimethylformamide
dissolved in 57 parts of cinnamic acid chloride was dropwise added at
10.degree. C. or below. The resulting mixture was stirred at 50.degree. C.
for 4 hours to give rise to a reaction. The reaction mixture was poured
into 500 parts of methanol to precipitate a polymer. The precipitate was
purified and dried under vacuum to obtain a polymer. The polymer was a
photocuring resin having cinnamoyl group as the photosensitive group and
had a resin acid value of about 81 mg KOH/g, a cinnamoyl group content of
3.69 moles/kg, a Tg of 51.degree. C. and a number-average molecular weight
of about 20,000. 100 parts of this polymer was dissolved in a mixed
solvent consisting of 50 parts of propylene glycol monomethyl ether and 50
parts of n-butanol, to obtain a photocuring resin solution.
EXAMPLE 1
181 parts (100 parts as solid content) of the photocuring resin solution
obtained in Production Example 1 was dissolved in 290 parts of ethyl
acetate. Thereto was added a solution of 1 part of LS-1 (a sensitizer)
(see Note 1) dissolved in 5 parts of benzyl alcohol, followed by stirring.
Thereto was added a solution of 1 part of T-1 (a polymerization initiator)
(see Note 2) dissolved in 5 parts of benzyl alcohol, followed by stirring.
Thereto was added a solution of 3 parts of N,N-dimethylaniline (a
radical-protecting compound) dissolved in 10 parts of benzyl alcohol,
followed by stirring, to obtain a uniform resist composition.
Note 1: LS-1 is a coumarin type sensitizer represented by the following
formula:
##STR5##
Note 2: T-1 is a titanocene type polymerization initiator represented by
the following formula.
##STR6##
The above-obtained resist composition was coated, by the use of a bar
coater, on a copper-clad glass fiber-reinforced epoxy substrate of 2 mm
(thickness).times.350 mm.times.460 mm having a 18 .mu.m-thick copper layer
on the surface. The coated composition was dried at 60.degree. C. for 10
minutes to obtain a dried resist film having a thickness of 10 .mu.m.
The above-obtained substrate having a resist film formed thereon was
subjected to scanning exposure via a 21 step-wedge film using a visible
laser (an Ar ion laser of 488 nm wavelength) so that the exposure became 3
mJ/cm.sup.2. The resulting material was heated at 60.degree. C. for 10
minutes and then immersed in a 1% aqueous sodium carbonate solution of
30.degree. C., to conduct development to remove the uncured portion of the
resist film. The sensitivity of the resist after development was Step No.
7 as measured using a 21 step-wedge film. Herein, the sensitivity of
resist was determined as follows. A resist was subjected to light exposure
via a film having a number of zones of gradually changing light
permeabilities (a 21 step-wedge film was used in the present invention),
and then to development; the Step No. of lowest light permeability which
gave a good resist pattern, was taken as the sensitivity of the resist.
Since a film zone of larger Step No. has lower light permeability, a
larger Step No. of lowest light permeability giving a good resist pattern
indicates higher sensitivity.
EXAMPLE 2
An operation was conducted in the same manner as in Example 1 except that
on the resist film of the substrate having a resist film formed thereon,
obtained in Example 1 was coated, by the use of a bar coater, an aqueous
solution containing 12% of a polyvinyl alcohol (polymerization
degree=1,700, Tg=65.degree. C., oxygen permeability=2.times.10.sup.-14 c.
cm/cm.sup.2. sec. cmHg) in an as-dried film thickness of 3 .mu.m; then,
drying was conducted at 60.degree. C. for 10 minutes to form a cover
coating layer on the resist film; the resulting material was subjected to
light exposure. The sensitivity of the resist after development was Step
No. 8.
EXAMPLE 3
An operation was conducted in the same manner as in Example 1 except that
the material after light exposure was heated at 60.degree. C. for 1 minute
using a hot plate. The sensitivity of the resist after development was
Step No. 7.
EXAMPLE 4
An operation was conducted in the same manner as in Example 1 except that
there was used a resist composition obtained as follows. 122 parts (70
parts as solid content) of the photocuring resin solution obtained in
Production Example 2 was dissolved in 290 parts of ethyl acetate. The
resulting solution was mixed with 30 parts of trimethylolpropane
triacrylate. The mixture was mixed with a solution of 1 part of LS-2 (a
sensitizer) (see Note 3) dissolved in 5 parts of benzyl alcohol. The
mixture was mixed with a solution of 7 parts of di-tert-butyl
peroxyisophthalate (a polymerization initiator) dissolved in 10 parts of
benzyl alcohol. The mixture was mixed with a solution of 3 parts of
N,N,2,4,6-pentamethylaniline (a radical-protecting compound) dissolved in
10 parts of benzyl alcohol, to obtain a uniform resist composition. The
sensitivity of the resist after development was Step No. 6.
Note 3: LS-2 is a coumarin type sensitizer represented by the following
formula.
##STR7##
EXAMPLE 5
An operation was conducted in the same manner as in Example 1 except that
the sensitizer LS-1 was changed to LS-3 (see Note 4). The sensitivity of
the resist after development was Step No. 6.
Note 4: LS-3 is a coumarin type sensitizer represented by the following
formula.
##STR8##
EXAMPLE 6
An operation was conducted in the same manner as in Example 1 except that
181 parts of the photocuring resin solution obtained in Production Example
1, used in Example 1 was changed to 200 parts (100 parts as solid content)
of the photocuring resin solution obtained in Production Example 3. The
sensitivity of the resist after development was Step No. 6.
COMPARATIVE EXAMPLE 1
An operation was conducted in the same manner as in Example 2 except that
no N,N-dimethylaniline as radical-protecting compound was used. The
sensitivity of the resist after development was Step No. 7.
EXAMPLES 7-15 AND COMPARATIVE EXAMPLE 2
Each operation was conducted in the same manner as in Example 4 except that
the kind and amount of radical-protecting compound used in resist
composition were as shown in Table 1 and that no radical-protecting
compound was used in Comparative Example 2. The sensitivity (Step No.) of
each resist after development is shown in Table 1.
TABLE 1
______________________________________
Radical-protecting compound
Step No. of 21
Amount step-wedge
Kind (parts) film
______________________________________
Example 7
N,N-Dimethylaniline
10 6
Example 8
N,N,2,4,6-Pentamethylaniline
1 5
Example 9
N,N,2,4,6-Pentamethylaniline
5 6
Example 10
N,N,2,4,6-Pentamethylaniline
10 6
Example 11
N,N-Dimethyl-m-toluidine
5 6
Example 12
4-Bromo-N,N-dimethylaniline
5 6
Example 13
2,6-Diisopropyl-N,N-dimethyl-
5 6
aniline
Example 14
Triethyl phosphite
5 5
Example 15
Triphenyl phosphite
5 5
Comparative
Not used -- 3
Example 2
______________________________________
EXAMPLE 16
The resist composition used in Example 1 was coated, by the use of a blade
coater, on a polyester film (to later become a cover film layer) having a
thickness of 25 .mu.m. The resulting material was dried at 100.degree. C.
for 4 minutes to form a visible light-curable photopolymerizable
composition layer having a thickness of 50 .mu.m. On this composition
layer was laminated a polyethylene film having a thickness of 35 .mu.m, as
a protective film to obtain a dry film resist. The protective film was
peeled, and the resist composition layer of the resulting material was
heat-laminated on the same copper-clad glass fiber-reinforced epoxy
substrate as used in Example 1, to obtain a substrate having thereon a
resist film and a cover film in this order. The material was subjected to
light exposure in the same manner as in Example 1; then, the cover film
was peeled; the resulting substrate having a resist film thereon was dried
at 60.degree. C. for 10 minutes and then subjected to development in the
same manner as in Example 1. The sensitivity of the resist after
development was Step No. 6.
As stated above, the resist film formed from the resist composition of the
present invention, when exposed to a visible laser, generates a radical;
however, the radical is not deactivated by oxygen because the resist
composition contains a particular radical-protecting compound, and
accordingly, the resist film can be prevented from the hindrance of curing
caused by the deactivation of radical by oxygen. Thus, a resist film of
high sensitivity can be formed by the use of the present resist
composition, and the resist film can be cured at high sensitivity even
without forming a coating cover layer or a cover film layer thereon. The
resist film can be cured at higher sensitivity by forming a coating cover
layer or a cover film layer thereon.
In general, when hindrance of curing takes place in a resist film because
of the presence of oxygen, the degree of curing of the resist film is
insufficient at around its surface; as a result, the resist pattern formed
has a semicylindrical sectional shape. However, with the present resist
composition, since the hindrance of curing caused by the deactivation of
radical by oxygen can be prevented, a resist pattern having a rectangular
sectional shape can be formed.
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